The present invention relates to an apparatus and to a method for the cleaning of substrates, especially semiconductor wafers.
Various methods and apparatus are known for the cleaning of semiconductor wafers. With one of these methods for the removal of organic contaminations, such as photo lacquer, the wafers are treated in a conventional wet cleaning process with sulfur peroxide mixtures (SPM) in order to remove the organic molecules. However, due to the chemicals that are used, this process is very cost intensive and furthermore has environmental problems during the removal of the used chemicals.
With a further method, which has a dry-cleaning process, gases containing O2 or H2 are used in order to remove fluorocarbon polymers from semiconductor wafers. Although no problems occur herewith due to the components that are used, such dry-cleaning processes are very time intensive, which leads to high costs.
A method is known from EP-A-0 867 924 according to which ozone gas is introduced into a steam or water vapor atmosphere that contains an additive in order to remove organic contaminations from a semiconductor wafer. In so doing, ozone is used to oxidize the contamination, and the steam promotes the oxidation process. With this method, the steam atmosphere is generated by heating and partially evaporating a water layer located below a wafer. The steam atmosphere is saturated at its operating temperature, which is greater than the temperature of the wafers. This causes a condensation of the steam upon the wafers, and a water layer forms upon the upper surface of the wafers. This water layer reaches a thickness that considerably disrupts an oxidation of the contaminations, since not only the ozone, but also OH radicals generated by interaction with the water, or other reactive components, do not come into contact with the contaminations. This is in particular the case if the thickness of the water layer is greater than the lifetime of the reactive components, such as ozone, times its diffusion constant in water.
Proceeding from the above mentioned method, it is an object of the present invention to provide an apparatus and a method that enables a rapid and effective cleaning of substrates in a simple and economical manner.
Pursuant to the present invention, this object is realized by an apparatus for the cleaning of substrates, especially semiconductor wafers, having a treatment tank for the accommodation of at least one substrate, a cover for the closing off of the treatment tank, a first introduction device for the controllable introduction of a reactive gas, a second introduction device for the controllable introduction of a moisture-containing fluid that promotes a reaction between the reactive gas and a contamination that is to be removed from the substrate, and a control device for the controlling of the moisture concentration in the treatment tank. The apparatus provides a closed system and enables a precise control of the concentration of moisture in the treatment tank. The moisture concentration can be adapted to the respective cleaning process, as a result of which the formation of a liquid layer on the substrates that are to be cleaned by the moisture-containing fluid can be prevented in a controlled manner or entirely. This is important in order to ensure that the reactive gas, or other reactive components, come into contact with the contaminations or impurities. Furthermore, the ratio of the reactive gas to the fluid can be set in order to provide an optimum cleaning atmosphere and to reduce the consumption of media. The closed system furthermore prevents an uncontrolled escape of the reactive gas/fluid mixture.
Pursuant to one preferred embodiment of the invention, the first introduction device has a valve for the control of the introduced quantity of gas, in order in this way to provide a controlled process atmosphere. The first introduction device preferably has an ozone generator, since ozone is particularly suitable and economical for the oxidation and removal of organic contamination.
In order to be able to control the concentration of moisture in the treatment tank in a simple manner, the second introduction device preferably has at least one valve for the control of the introduced quantity of fluid. The second introduction device preferably has a vapor generator, especially a water vapor, i.e. steam generator, since steam is easy to produce and can be used as a reaction-promoting fluid. In this connection, the moisture concentration and/or temperature of the vapor is preferably controllable.
Pursuant to a particularly preferred embodiment of the invention, the second introduction device has at least one liquid inlet nozzle. Since a specific quantity of a liquid is introduced into the treatment tank, the moisture concentration can be established in a simple manner. In this connection, the liquid inlet nozzle is preferably disposed above the substrates and is directed onto them in order to enable a rinsing of the substrates. In particular, the oxidized reaction products are rinsed off of the wafers in order to expose the non-oxidized layers disposed there below.
For the control of the process atmosphere, in particular also the concentration of moisture in the treatment tank, the apparatus preferably has a heating device for the heating of the treatment tank and/or of the tank contents, a controllable withdrawal device, and/or a controllable liquid outlet.
To further enhance the reaction of the reactive gas, or to optimize the process conditions, the apparatus has a third introduction device for the controllable introduction of a further fluid, especially a wetting agent.
To permit the controlled displacement of the process components out of the treatment tank, and thus prevent their escape into the atmosphere when the tank is opened, a further gas introduction device is preferably provided for the controllable introduction of a further gas, especially an inert gas.
For a precise setting of the moisture concentration, a device is provided for the measurement of the concentration of moisture in the treatment tank. This enables a feedback of the actual moisture concentration to the control device, which in conformity therewith can adapt its control parameters.
Pursuant to a particularly preferred embodiment of the invention, the treatment tank is pressure tight and the apparatus has a pressure control device that is suitable for controlling the pressure in the treatment tank to an overpressure. By using an overpressure in the treatment tank it is possible to use steam or vapor having a greater temperature, which promotes a reaction and thus accelerates the progress of the process. Furthermore, by means of the pressure it is possible to control the concentration of moisture in the treatment tank, as well as to control the boundary layer or interface between substrate surface and process atmosphere. By the use of overpressure, there thus results a good controllability of the moisture concentration as well as a shortened process time, as a result of which the throughput of the apparatus is increased. In this connection, the treatment tank is preferably sealed in a pressure tight manner by the cover in order to achieve a good seal relative to the surrounding atmosphere. The danger that ozone escapes from the treatment tank is prevented, as a result of which the use of greatly concentrated ozone is possible without a danger to the environment. The use of greatly concentrated ozone leads to an increased reaction rate, as a result of which the process times can be reduced still further.
The object of the invention is also realized by a method for the cleaning of substrates, especially semiconductor wafers, in a treatment tank for the accommodation of at least one substrate, with the following method steps:
Introducing a substrate into the tank; closing off the treatment tank; introducing a reactive gas and at least one moisture-containing fluid that promotes a reaction between the reactive gas and a contamination that is to be removed from the substrate; and controlling the concentration of moisture in the treatment tank. As a result of this method, the advantages already mentioned above in conjunction with the apparatus are achieved.
To achieve a control process atmosphere, the quantity of the introduced reactive gas and/or of the fluid are preferably controlled.
Pursuant to one embodiment of the invention, a fluid is vapor, especially steam, the moisture and/or temperature of which is controlled. To avoid the formation of a liquid layer upon the substrate, and the drawbacks connected therewith, the process atmosphere in the treatment tank is preferably controlled in such a way that essentially no condensation of the vapor upon the substrate occurs. Pursuant to one embodiment of the invention, for this purpose the temperature of the substrate is held at or above the temperature of the vapor. The vapor is preferably introduced into the treatment prior to the reactive gas, especially ozone.
To maintain constant process conditions, and to enable the supply of unused media, at least a portion of the mixture of reactive gas and fluid found in the treatment tank is drawn out. For this purpose, the quantity of the withdrawn mixture is preferably controlled.
In order in addition to the maintenance of a moist process atmosphere to enable a rinsing of the substrates and a good mass transfer, a fluid is preferably a liquid. Advantageously at least a portion of the liquid is withdrawn in order to maintain uniform and controlled process conditions. In this connection, the quantity of the withdrawn liquid is preferably controlled. For a good rinsing, the liquid is preferably sprayed onto the substrate from above. This process is preferably effected during short time intervals in order to prevent the uncontrolled formation of a liquid layer upon the substrate. In this connection, the time intervals for the spraying are preferably considerably shorter than the intervals there between.
For a good control of the process atmosphere, the temperature of the treatment tank and/or the tank contents are preferably controlled. The moisture content is preferably controlled with the aid of the quantity of the introduced reactive gas, the quantity of the introduced fluid and/or the temperature. Pursuant to one embodiment of the invention, the concentration of moisture in the treatment tank is measured and is regulated with the aid of the measurement results.
To prevent an escape of the reactive mixture of gas and fluid when the treatment tank is opened, the reactive mixture is withdrawn after the cleaning. Pursuant to one embodiment of the invention, after the cleaning a further gas, especially an inert gas, that displaces the reactive gas is introduced into the treatment tank. Pursuant to a further embodiment, after the cleaning a treatment liquid is introduced into the treatment tank in order to further treat the substrate. Since the treatment liquid is introduced directly into the treatment tank, a handling and a transport of the substrates into a further treatment unit is eliminated, thereby eliminating the danger of damage to the substrates during the handling and/or the transport.
The inventive apparatus and the inventive method are particularly suitable for the removal of organic contaminations, such as photo lacquer, from semiconductor wafers.
Pursuant to a particularly preferred embodiment of the invention, the pressure in the treatment tank is controlled, in particular is controlled to an overpressure, as a result of which high vapor temperatures can be achieved during the treatment.
Furthermore, by means of the pressure a control of the concentration of moisture in the treatment tank is possible.